Buttermilk, yogurt, sour cream, and crème fraîche are all dairy products that have a characteristic sour and tangy flavor due to the addition of a bacterial culture or lactic acid. After the addition of the culture, these products are heated, allowing the bacteria to convert the sugars to lactic acid, resulting in a pleasant tart flavor and prolonged shelf life.
Buttermilk
In times past, buttermilk was the by-product of making butter; however, modern buttermilk is produced through the addition of a bacterial culture to whole, low-fat, or nonfat milk, giving it a thickened, tangy flavor.
Yogurt
A cultured dairy product made from whole, low-fat, or nonfat milk to which a bacterial culture is added. Greek- or Icelandic- style yogurts are strained for a richer texture.
Mascarpone
This Italian cheese has a high butterfat content ranging from 70 to 75 percent. It is an ivory-colored, firm-bodied, mildly sweet cheese. However, mascarpone is not technically a cheese, as it is produced by the addition of an acid to cream, which is heated, causing it to thicken.
Polenta Cake with Grappa, Berries, and Minted Mascarpone
Crème Fraîche
A cultured dairy product widely used in France and traditionally produced by allowing the natural bacteria present in unpasteurized cream to thicken and sour it at room temperature. In the United States, crème fraîche is made from cream containing 30 to 40 percent butterfat, and is produced with the addition of a bacterial culture. Crème fraîche has a mildly tangy, nutty flavor with a smoother, richer texture than sour cream.
Cardamom-Poached Pears with Crème Fraîche
Sour Cream
The characteristic tangy flavor is created by adding lactic acid to cream containing 18 to 20 percent fat to thicken it. Often gums, gelatin, or starches are added to create a gelled consistency. Low-fat or light sour cream has a fat content of approximately 10 to 11 percent, and often can be used as a substitute for full-fat sour cream in fillings and garnishes without compromising flavor or texture.